How to make a PDF smaller to email or upload, on Mac, Windows and iPhone

Why some PDFs are so big

A PDF made from typed text is tiny, often a few KB a page, because it stores letters rather than pictures. A PDF made by scanning or photographing paper is different: every page is an image. A phone photo of one page can be 3–5 MB, so a short scanned document can easily reach 10–20 MB.

The size depends on three things, roughly in this order: how many pixels each page has, whether it’s in color, and how many pages there are. Change those and the PDF shrinks.

How small does it need to be?

• Email: Gmail allows attachments up to 25 MB per email, and Outlook typically around 20 MB.
• Online forms: many set limits of 1–5 MB; some, including many government and exam portals, ask for 100–500 KB.

How to make a PDF smaller on a Mac (Preview)

1. Open the PDF in Preview and choose File → Export.
2. Set Quartz Filter to Reduce File Size and save under a new name.
3. Open the new file and zoom to 100%. The filter can compress hard; if text has gone fuzzy, use the scan method below instead.

How to make a PDF smaller on Windows

• From a Word document: choose File → Save As, pick PDF, and set Optimize for to Minimum size (publishing online).
• From photos or scans: resize the page images first, select them in File Explorer, right-click, choose Print (under Show more options on Windows 11) and pick Microsoft Print to PDF.
• With Adobe Acrobat: Acrobat has its own compress or reduce file size option.

How to make a PDF smaller on iPhone and Android

1. Photograph each page, then resize and compress the images; Bulk image resizer does all the pages at once in your browser.
2. iPhone: in the Files app, select the images, tap the More button and choose Create PDF. Android: open the images and choose Print → Save as PDF, or scan with the Google Drive app.
3. Check the size, then open the PDF at 100% zoom.

Getting a scan under 100, 200 or 500 KB

For strict upload limits, divide the limit by the number of pages and leave some room for the PDF itself.

A grayscale letter or A4 page at 150 DPI is about 1,275 × 1,650 or 1,240 × 1,754 pixels, and usually fits within 100–200 KB as a JPG while staying easy to read. For a 100 KB single page, go to about 1,000 pixels on the long side.

Scan smarter

• Resolution: 150–200 DPI is readable for most printed documents; keep 300 DPI for very small print.
• Color: scan black-and-white documents in grayscale; use color only where it matters, such as a photo ID.
• Margins: crop away the table, your fingers and empty margins.

Make a PDF smaller without losing quality

For documents, “quality” means every word is readable at 100% zoom. Get there by cutting pixels and color you don’t need, not by squeezing the compression: a 150 DPI grayscale page stays crisp, while a 300 DPI color page compressed hard to the same size turns blotchy. If a form also sets a minimum size, scan at a higher resolution rather than adding blank pages.

Anekvio PDF tools are next

A tool that compresses a PDF to a size limit on your own device is next on Anekvio’s workbench, followed by merging, splitting and converting between images and PDF. If your form or email has a limit we should build for, tell us about it.

Questions people ask

How do I make a PDF smaller to email?

On a Mac, export it from Preview with the Reduce File Size Quartz filter. From Word, save as PDF with Minimum size. For scans, rebuild the PDF from smaller page images.

How do I reduce PDF size on Mac without losing quality?

Try Preview’s Reduce File Size filter first and check the text at 100%. If it’s fuzzy, rescan or rebuild the PDF from page images resized to about 150 DPI instead.

How do I compress a PDF to 100 KB?

For a one-page scan, resize the page image to about 1,000 pixels on the long side, in grayscale if possible, compress it to around 90 KB, and save it as a PDF.

Why is my scanned PDF so large?

Each page is stored as a full-size picture. Fewer pixels, grayscale and cropped margins shrink it the most.